We should make this easy:
Assume the following moves for the following categories.
Dragon STAB: Clanging Scales, Dragon Pulse, Draco Meteor
Poison STAB: Sludge Wave, Sludge Bomb
Setup: Clangorous Soul
At least one from the following categories:
Fire Coverage: Fire Blast, Flamethrower
Water Coverage: Hydro Pump, Surf, Sparkling Aria (this moves realistically is just Surf but I know some folks want to max out our sound moves)
Fighting Coverage: Close Combat, Aura Sphere, Focus Blast
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Defining moves is not the movepool stage, its sole purpose is to allow folks to justify the stats spreads that they're submitting, and I don't see a huge reason to overcomplicate things. The list above imo gives about every major permutation of a Throat Spray Clang Soul set, with various relevant coverage moves, and choice of coverage will help to justify differing SpA stats.
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The only things that are not on the above list that could be defining moves, specifically optional defining moves, are, in my opinion, the following.
Boomburst is functionally as strong as Sludge Wave post-stab, and gives us very broad neutral coverage. I really don't love it here, as Sludge Wave well, does a fairly good job with Dragon, but Dragon/Fire/Normal and Dragon/Water/Normal are very very competent typings in combo with eachother, and a Tera-Normal set with Boomburst would be quite potent. I can 100% see this move as an optional defining move, though again I personally don't love it.
Recover clones are a fairly obvious route forward; Clang Soul has a major HP cost and increases defenses, Recover mitigates the HP loss, and abuses the increased defenses to potentially get +2 instead of +1. That said, our typing really does not do well on a 2 attack / recover / setup kinda route, as we're forced into Dragon/Fire, Dragon/Water, or some other similar route, all of which have major issues breaking past major mons in the meta.
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Torch Song seems just straight up worse than Fire Blast here? +3 Torch Song is about 10% weaker than +2 Fire Blast, and this is a setup sweeper that is likely to fit on fairly hard offense structures. We are almost guaranteed to care more about our ability to chunk Libra for 80 and then die, than the potential to go for a very long game. Our ability to inflict major damage after a single turn of setup, and either abuse our teammate's prior work weakening a wall, or to heavily weaken a wall for a teammate is more important than our ability to put out long term damage.
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Frankly when it comes to designing stat spreads, I'm not really sure if we need that many defining moves? This mon, as it is, is a very simple mon to design.
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Edit:
Thinking more, probably just say "any reasonably distributed Fire, Water, or Fighting type move" just because part of my brain wants to give this mon every single pledge move.